title: The modulation of spinal growth with nitinol intervertebral stapling in an established swine model.
abstract: OBJECTIVE
  Anterior spinal stapling for the treatment of adolescent idiopathic scoliosis has been shown to slow progression in small curves; however, its role in larger curves remains unclear. The purpose of this study was to evaluate the effectiveness of nitinol staples to modulate spinal growth by evaluating the two-dimensional and three-dimensional morphological and histological effects of this method in a well-established porcine model.
  
  
  METHODS
  Three immature Yucatan miniature pigs underwent intervertebral stapling. Two staples spanned each of three consecutive mid-thoracic discs and epiphyses. Monthly radiographs were obtained. Computed tomography (CT) was conducted at harvest after 6 months of growth. Measurements of wedging and height for each disc and vertebral body were conducted. Micro CT was used to compare physeal closure between stapled and non-stapled levels. Histology of the growth plate also compared the hypertrophic zone thickness for control and stapled vertebrae.
  
  
  RESULTS
  After 6 months of stapled growth, the average coronal Cobb angle of the stapled segments increased by 7.7 ± 2.0° and kyphosis increased by 3.3 ± 0.6° compared to preoperative curves. Increased vertebral wedging and decreased disc height (p < 0.001) were noted in stapled regions. Overall, 26 ± 23 % of each growth plate was closed in the stapled segments, with 6 ± 8 % closure in the unstapled levels. No difference was observed regarding the hypertrophic zone height when comparing instrumented to uninstrumented levels, nor was a difference recognized when comparing right versus left regions within stapled levels alone.
  
  
  CONCLUSIONS
  Six months of nitinol intervertebral stapling created a mild coronal and sagittal deformity associated with reduced vertebral and disc height, and increased coronal vertebral and sagittal disc wedging.
authors.affiliation: Department of Orthopaedic Surgery, University of California, San Diego, 200 West Arbor Drive, San Diego, CA 92103 USA.
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Carreau
authors.forename: Christine L
authors.initials: CL
authors.lastname: Farnsworth
authors.forename: Diana A
authors.initials: DA
authors.lastname: Glaser
authors.forename: Joshua D
authors.initials: JD
authors.lastname: Doan
authors.forename: Tracey
authors.initials: T
authors.lastname: Bastrom
authors.forename: Nathan
authors.initials: N
authors.lastname: Bryan
authors.forename: Peter O
authors.initials: PO
authors.lastname: Newton
keywords: Growth modulation; Nitinol; Scoliosis; Spinal stapling; Spine stapling